1. Field of the Invention:
This invention relates to a hydrated silica gel for stabilization treatment of beer for improving the haze stability of beer, and more specifically to a hydrated silica gel as a filtration aid for providing good quality beer which does not generate haze, for example, even when beer is stored for a prolonged time after being packed into bottles (or cans or barrels).
2. Description of the Prior Art:
Beer is a fermentation product produced from (malt of) barley and hop as main starting materials, and in the case of light-colored beer, its amber-colored, bright and transparent appearance is also one of great product characteristics. However, if the stability of beer is not adequate, when the beer is stored for a prolonged time after packed into bottles (or cans or barrels) or when it is cooled for drinking, it causes haze and therefore there is a problem that its product value is deteriorated.
This haze is more specifically classified into three: chill haze which is brought about when beer is cooled to about 0.degree. C. but solubilized again when warmed to 20.degree. C.; permanent (or oxidized) haze which is no longer solubilized even when beer is warmed to 20.degree. C.; and frozen haze which is brought about when beer is frozen or stored at a temperature near the freezing point (-5.degree. C.). Of those, what dominate the product value of beer are cold haze and permanent haze, and these haze are brought about by a change in the beer components, and generated by the association of colloidal components such as certain proteins, polyphenols etc. Further, this tendency shows that the longer the storing period of beer, the higher the degree of haze, since the affinity to the proteins is increased when the polyphenols are oxidized. The colloidal components of these proteins, polyphenols etc. are derived from the starting materials, i.e., barley, hop etc. and hence are inevitable components in beer and thus this problem is inherently present with beer.
Therefore, in order to prevent the haze of beer, it is necessary to reduce these colloidal components causing these haze in beer, and it has heretofore been generally employed for this purpose, for example, a method which comprises treating beer with a haze inhibiting (stabilizing treating) agent such as papain, tannic acid, PVPP (polyvinyl polypyrrolidone), silica gel etc. Inter alia, the silica gel is widely used since it does not exert great influences on the taste, foam or other qualities of beer.
For example, British Patent No. 938,153 discloses the use of an acid-treated silica xerogel which has a specific surface area of 200-400 m.sup.2 /g, a pore volume of 0.6-1.2 ml/g, a pore diameter of 60-150 .ANG. and a pH as its 5% aqueous suspension of 4.5-7.0 when clarifying beer, and further British Patent No. 98175 also discloses the use of an acid-treated silica xerogel which has a specific surface area of 200-600 m.sup.2 /g, a pore volume of 0.5-1.5 ml/g, a pore diameter of 40-180 .ANG. and a pH as its 5% aqueous suspension of 4.0-8.0 when clarifying beer. Furthermore, British Patent No. 1279250 discloses the use of a silica xerogel which has a specific surface area of 700-1200 m.sup.2 /g, a pore volume of 0.7 ml/g or more and a mean pore diameter of 25-80 .ANG. when clarifying beer, and British Patent No. 1215928 discloses the use of a silica hydrogel which has a specific surface are of 700 m.sup.2 /g or more, a mean pore diameter of 30-120 .ANG. and a pH as its 5% aqueous suspension of 1.5-2.0 when clarifying beer. However, in the case of the known silica xerogel or silica hydrogel as described above, although some effect could be obtained, it has not been satisfactory. In short, in the case of silica gel, various types having different physical property values may be obtained depending on the production conditions, but when these are applied to the stabilization treatment of beer, the basic principles reside in:
1. selective adsorption and removal of proteins (or association products thereof with polyphenols) which are one of colloidal components causing haze due to the surface silanol groups, and
2. selective capture and removal of substances causing the formation of haze by a gel permeation mechanism based on the pore structure and the pore diameter distribution, and therefore it is necessary to precisely select the respective physical property values of the silica gel suitable for the beer treatment.